A widely used medium for storing data is recording tape, which is typically a polymer tape with a magnetic coating. One of the most popular formats of use for the storage of data on tape is tape cartridges. Tape cartridges are generally smaller, simpler and less expensive than reel-to-reel tape systems.
Two widely used formats of tape cartridges are the two-reel cartridge, which is typically in a quarter-inch tape format, and the single, supply-reel cartridge, generally a half-inch tape format cartridge. By enclosing the tape within a housing or cartridge, the tape, and therefore the data stored on the tape, are better protected from damage than the more exposed reel-to-reel systems of tape data storage.
The single, supply-reel or half-inch cartridge is able to store much more data than the quarter inch cartridge. Typically, the free end of the tape in the cartridge is attached to a leader block. The leader block is fashioned to act as a barrier or door when the cartridge is not in use, and thereby substantially close off the cartridge from potential sources of harm such as dust, particulate matter contamination and other forms of environmental stress or damage. When the cartridge is in use, the leader block's function is to provide a structure to allow the tape to be withdrawn from the cartridge, into the tape drive for data recording or retrieval. The take-up reel or spool is built into the tape drive along with an automatic tape threading mechanism. The automatic tape threading mechanism includes a means for capturing the leader block, typically the capture is by a tape threading pin, and then the mechanism appropriately threads the leader block and tape in the tape drive.
The recording of data onto the tape is generally referred to as "writing" to the tape and the retrieval of information already written or stored on the tape is referred to as "reading" from the tape. The part of the tape system responsible for these activities is generally referred to as the read/write head. The tape drive that performs the read/write operations is also referred to as a tape "transport."
Typically, the standard tape transport or drive accepts the tape cartridge into an elevator assembly. A threading mechanism grabs the leader block and pulls it free from the cartridge. The leader block is then used to thread the tape through a path which includes a series of guide posts, across the longitudinal read/write head, and into a slot in the take-up reel. Once threaded, the tape from the cartridge can be driven across the read/write head(s) for data transfer operations and wound onto the take-up reel.
The take-up reel is typically configured with a slot in one surface that allows the insertion of the leader block into the hub of the take-up reel in a manner that, ideally, allows the tape to wind smoothly onto the take-up reel. The leader block is captured by a threading pin attached to a threading or threader arm assembly. The threading arm then pulls the leader block in a counter-clockwise direction through the tape path and inserts the leader block into the hub of the take-up reel. During winding on of the tape onto the take-up reel, the leader block spins around the threading pin, as the pin and the take-up reel have the same axis of rotation in this configuration. When the leader block is fully inserted into the take-up reel, the leader block forms a part of the outer circumference of the take-up reel and thus, the magnetic tape winding surface. The leader block and take-up reel are fabricated with a degree of precision so that when the leader block is inserted into the slot in the take-up reel, the slot is closed by the end of the leader block so that a relatively smooth surface is created on the hub of the take-up reel for winding the tape on the hub.
Ideally, the tape cartridge, or housing and all of the components are designed and manufactured to promote the best possible storage and retrieval of data on the tape. One important goal in the design and manufacture of the components is to have the tape wind smoothly through the drive and onto and off of both the supply reel and the take-up reel. Unfortunately, there are numerous potential hazards in the structures and functions of the single reel tape system that make obtainment of consistently smooth tape winding problematical. Any misalignment of the magnetic tape within the system can result in a non-uniform tape winding surface which causes undesirable irregularities in the magnetic tape as it is wound or unwound from either reel. Small misalignments between the inserted leader block and the hub are commonplace and represent a source of undesirable risk of failure in tape systems. Such misalignments can garble data and operations, causing errors in either or both the writing of data to the tape and reading of data from the tape.
Improvements in the functioning of the tape storage and retrieval system are constantly sought to decrease sources of error and failure in data storage and retrieval. Whenever data is transmitted and wherever it is stored, it is vulnerable to many different forces and conditions that can physically distort the record, changing the character of the data. Any source of error is problematical to the accurate and successful recording and retrieval of data to and from the tape. Irretrievable data can be catastrophic at worst and is always undesirable. The consequences can be devastating; for example, as little as a single wrong data bit can change the meaning of an entire sequence of bits, perhaps throwing off a complex mathematical calculation or causing a computer to misinterpret a command. The sources of risk for error and failure are under constant scrutiny for reduction and elimination in the industry. A combination of strategies may be best to safeguard the data from the inevitable assault of errors.
One place in the system where an impediment to smooth winding tape can develop is the supply reel, in the tape cartridge. When the cartridge is not in use in a tape drive, it is possible in some cartridges for the tape to lose tension and become partially unwound from the reel. When the tape is loose and unwound, it is possible for the tape to loop back on itself. The tape can be damaged as a result of the loose wraps and misalignments, for example, the recording side of the tape coming in contact with itself and causing damage. Loose or misaligned tape on the reel can also be damaged by sharp creases being put in the tape, if the looped-back sections inadvertently become trapped and rewound tightly and under tension on the supply reel or through snapping and possibly breaking the tape when tension is restored to the tape in the cartridge. To prevent problems and failures caused by this nature of problem, one solution has been to add additional structures to the cartridge. For example, spring-biased catches, that grab either an added brake structure, or the drive gears that are integrated on the reel, for engagement with the torque motor when in the tape drive, have been utilized. Such structures do help to reduce the likelihood of the tape coming loose off the supply reel, but the additional structures also come with their own characteristic disadvantages. Every added structure adds undesirably to the cost and complexity of the system. Added structures also represent their own potential basis of system failures, in the form of malfunctioning or broken parts and components.
There is still a demand and need for methods and apparatus to reduce the possible sources of error in tape recording systems.